1. Field of the Invention
The present invention relates to magnet-based sensors and in particular magnet-based magnetostrictive sensors.
2. Description of the Prior Art
Magnetostrictive transducers having elongated wave guides that carry torsional strain waves induced in the wave guide when current pulses are applied along the wave guide through a magnetic field are well known in the art. A typical linear distance measuring device using a movable magnet that interacts with the wave guide when current pulses are provided along the wave guide is shown in U.S. Pat. No. 3,898,555.
Devices of the prior art of the sort shown in U.S. Pat. No. 3,898,555 also have the sensor element in a housing which also houses the electronics to at least generate the pulse and receive the return signal. The amplitude of the return signal detected from the acoustical strain pulse is, as well known in the art, affected by many parameters. These parameters include the position magnet strength, wave guide quality, temperature, wave guide interrogation current, and assembly tolerances. In the prior art, the wave guide is connected to a return wire to complete the electrical circuit necessary for the wave guide to generate the pulse which stimulates the return signal.
Several types of magnetic-based sensors are available for measuring linear or rotary position. Magnetic-based sensors have an advantage in that they provide non-contact sensing; so there are no parts to wear out. Examples of magnetic-based sensors are LVDTs, inductive sleeve sensors, and magnetostrictive sensors.
A difficulty in the prior art was attaching the return wire to the wave guide in a magnetostrictive application. It normally required a lengthy, involved soldering process. Welding and crimping processes are also possible, but the welding process also is complicated and the crimping process has not been developed to the point where it is reliable without inspection. Nevertheless, those in the prior art have exclusively used a return wire.
It is an object of the present invention to utilize magnetostrictive interrogation without a return wire.